A series of high-profile incidents has triggered a public debate about safety within the rapidly growing industry. — SCMP
A series of electric vehicle fires in China has pushed the issue of battery safety into the public spotlight, triggering a wider public debate about the potential risks.
Last month saw a number of high-profile incidents, including one on Oct 13 in Chengdu, the capital of Sichuan province, where a Xiaomi EV burst into flames after a high-speed crash, killing the driver.
On Oct 23 in Shanghai, a Li Auto car suddenly burst into flames on a bumpy road, becoming fully engulfed within 10 seconds. The occupants escaped.
A week later in Hong Kong’s Kwun Tong district, firefighters had to put out a blaze after smoke emerged from a BYD car parked in an indoor garage.
Xiaomi, Li Auto and BYD have all been asked for comment.
Such incidents, which have affected almost all EV makers in the past, have prompted a debate about the safety of the batteries used in the vehicles, with some social media users saying they have been having second thoughts about buying the vehicles because of safety concerns.
Other manufacturers, including Tesla, Nissan, BMW and Hyundai, have previously had to recall vehicles due to battery safety concerns.
China’s electric vehicle market has been growing rapidly. According to data from the China Passenger Car Association, there were 1.4 million new EV retail sales last month, a year-on-year increase of 17% and an 8% increase on the previous month.
Cumulative retail sales this year have reached 10.3 million, up 23% compared with the same period last year.
Additionally, customs data shows that from January to September this year, China exported almost 5.7 million vehicles, a year-on-year increase of 20.9%, a figure forecast to rise to 7 million this year.
Most electric vehicle fires originate from a process known as a “thermal runaway” in the battery.
It is usually triggered by physical damage caused by a direct impact, but other causes can include manufacturing flaws, prolonged exposure to the sun in hot weather or overcharging.
A short circuit in the lithium-ion batteries can generate intense heat. In the case of crashes, this is typically caused by the casing in the batteries being crushed or punctured.
The rising temperature then triggers a reaction within the battery that releases flammable gases such as methane or hydrogen.
Finally, the problem spreads. Heat from one burning cell moves to the next, causing a domino effect. The entire battery pack can be engulfed in flames within seconds.
An investigation by Li Auto into last month’s Shanghai fire suggested that a coolant with inadequate corrosion resistance had leaked and triggered the thermal runaway process. The firm issued a recall notice for around 11,400 vehicles that were at risk of a similar fault.
Electric vehicle fires are often difficult to extinguish due to fundamental differences from fires in petrol-fuelled cars.
Some lithium battery cathode materials decompose at high temperatures, releasing oxygen and creating a self-oxygenating burn that can sustain itself even without external air.
A further problem is that the blazes start inside sealed battery cells that fire suppressants struggle to penetrate.
This often leaves continuous cooling as the only way to control the blaze. On-board fire suppression systems using dry powder or aerosol agents are generally only effective during the initial stages of a fire.
The two main types of electric car batteries, ternary lithium and lithium ferro phosphate (LFP), have key safety differences.
Ternary lithium batteries have a higher energy density, which helps cars perform better in cold weather and gives them a longer range.
However, they are less safe because they contain reactive metals and can catch fire at temperatures below 200 degrees Celsius (392 degrees Fahrenheit), leading to more intense fires.
LFP batteries are much safer. They can withstand temperatures above 500 degrees Celsius before failing and are highly resistant to fires caused by damage or overcharging.
They also last for more charging cycles. The main downside is their lower energy density, meaning a larger, heavier battery is needed for the same driving range.
China has been strengthening its safety regulations and technical standards for batteries for some time.
The existing safety standard states that a battery pack must not catch fire or explode for at least five minutes after thermal runaway begins.
New regulations, described as the strictest in the industry and set to come into force in July next year, significantly tighten these rules.
They say that within a two-hour testing period there must be no fires or explosions. It also introduces a new test for what happens when the bottom of the car is hit, for example on bumpy roads.
Future solid-state batteries are seen as a promising solution because they eliminate the risk of electrolyte combustion, are hard to short circuit inside and are more stable at high temperatures.
In March, China officially began establishing a national standard for electric vehicle solid-state batteries.
Meanwhile, some semi-solid-state batteries have already entered mass production and are being installed in vehicles. – South China Morning Post
